1. Field of the Invention
The invention relates in general to elevator systems, and more specifically to new and improved car call stations and circuitry for elevator cars.
2. Description of the Prior Art
There are various circuit arrangements used in the prior art for registering car calls on the car call push button station located in the elevator car. For example, the push buttons for registering car calls in the car stations may be wired using DC, and the button is grounded to register a call. If a call wire in the hatch trail cable is shorted to ground for some reason, a call would be falsely registered. If this occurs during a fire emergency, a call could be falsely registered for the floor of the fire.
In another arrangement, a combination of AC and DC is used. Positive DC registers the car call and AC shows "re-registering" of the call. In these systems an AC relay, a special transformer, and additional wiring in the control cabinet is required. Further, a relay per pushbutton is also required.
U.S. Pat. No. 3,519,106 which is assigned the same assignee as the present application, discloses a new and improved pushbutton circuit arrangement for registering calls for elevator service and for driving the associated lamp, which circuit arrangement reduces the amount of wiring required by using opposite polarity pulses and a common transmission channel for the pulses. When the pushbuttons are in the car call station located in the elevator car, the pushbuttons are each provided with a second set of contacts. The second set of contacts of each pushbutton is connected to provide a "button actuated" signal for the door circuits. The door circuits utilize the signal to shorten or cut out the remaining door non-interference time. The "button actuated" signal must be provided each time a pushbutton is actuated, i.e., when the button is actuated to register a call, and also when it is actuated after the call is placed and the associated lamp energized.
When an elevator car stops for a hall call, the door remains open for a predetermined period of time, referred to as the door non-interference time. When the prospective passenger, or passengers, enter the car and place a car call on the car call pushbutton station, the placing of the call is a good indication that all passenger transfers have been made. Trip time may thus be reduced by shortening, or cancelling any remaining non-interference time and initiate door closure immediately. If an incoming passenger desires to travel to a floor for which a car call has already been registered by a passenger during a prior stop, actuating this pushbutton again should also function to shorten or cancel the remaining door non-interference time. The extra set of contacts in each pushbutton of the car call station of the hereinbefore mentioned U.S. Patent performs this function.
Pushbuttons with two sets of contacts, however, have not proven to be as reliable as desired. For example, if the pushbutton is not pressed directly in its center, it is possible for one or the other of the two sets of contacts to make, resulting in a car call being registered without a reduction in door open time, or a reduction in door open time without a call being entered. Thus, it would be desirable to be able to register a call and provide a "button actuated" signal each time the pushbutton is actuated, while using only a single set of contacts. Further, it would be desirable to do this, and to drive the associated lamp, while utilizing a single or common transmission channel or conductor between each pushbutton/lamp combination and the associated car call control station.